The relationship between left ventricular functional response to isometric exercise and asynergic contraction and diastolic stiffness

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Abstract
Either augmentation or impairment of left ventricular function has previously been reported in different patients, in response to isometric exercise. To identify the mechanisms associated with these disparate responses, the effects of submaximal sustained handgrip upon left ventricular systolic and diastolic properties were studied in 29 patients during diagnostic catheterization. In 16 patients (group I), ejection fraction, mean Vcf, and the mean systolic ejection rate remained constant, while the ratio of peak systolic pressure to end systolic volume increased significantly from 2.81 ± 0.6 to 3.17 ± 0.6 ml/mm Hg. In 13 patients (group II) ejection fraction declined from 0.6 ± 0.03 to 0.51 ± 0.03, Vcf from 0.96 ± 0.09 to 0.85 ± 0.09 circ/sec, mean normalized systolic ejection rate from 1.79 ± 0.1 to 1.50 ± 0.09 sec−1, and the peak systolic pressure to end systolic volume ratio from 2.23 ± 0.3 to 1.99 ± 0.3 (p < 0.05 for each). Systemic arterial mean pressure increased similarly by 19% and 21 % in groups I and II, respectively (p < 0.05 for each). Systemic vascular resistance increased significantly by 23% in group I and by 5% in group II (p < 0.05). Left ventricular end diastolic volume declined from 85.4 ± 7 to 77.3 ± 11 ml/m2 in group I, while end diastolic and end systolic volumes increased by 13% and 35%, respectively in group II (p < 0.05 for each). In both groups, baseline exponential pressure‐volume relations were similar, though higher intercepts of the pressure‐volume relations upon the Y‐axis suggested greater “diastolic tone”, and steeper volume‐normalized pressure‐volume elasticity relations indicated “stiffer” left ventricular chambers in group II patients. While the incidence of coronary artery disease was similar, both the severity and extent of left ventricular asynergy were greater in group II patients. We conclude that dilatation and deterioration of left ventricular ejection function in response to isometric exercise are causally related to, and comprise a useful predictor of, severe underlying left ventricular asynergy and impaired chamber distensibility.